Integrierte Vermeidung und Verminderung der Umweltverschmutzung

Chapter 2
The main raw materials used in Europe for the production of starch and its derivatives are
cereals, i.e. maize, wheat, barley and rice, and potatoes of dedicated varieties. Each installation
is usually technically dedicated to one raw material [10, Environment Agency of England and
Wales, 2000, 84, European Starch Association, 2001]. Only starch production from maize,
wheat and potatoes is described in this document.
2.2.8.1 Maize starch
The commercial separation of pure starch from maize is achieved by a wet milling process
which is generally considered to be efficient. The process is operated as an enclosed system in
which process water is re-used in a closed circuit. The addition of fresh water is limited to one
point in the production process.
The raw material is washed using aspiration and screening to remove dust, chaff, broken grain,
cobs and other extraneous material. The maize is soaked in water with sulphur dioxide (SO2) or
sodium bisulphite (NaHSO3), for around 36 hours, in a process known as steeping. This
removes solubles in the maize, softens the kernel to improve separation of the various
components and reduces microbial activity. After steeping, the maize is passed through several
grinding and separation operations until only starch and gluten remain. The grain is first ground
coarsely and the germs are removed from the coarse grist. After removing the germ, the grist is
finely ground and fibre is removed through a screening operation. Starch and gluten are
separated, typically using centrifugal methods. This raw starch is washed with drinking water,
using a countercurrent flow, in a series of four to six centrifuges. At one end, raw starch is the
input and process water is the output and at the other end, refined starch is the output and fresh
drinking water is the input. The starch, which at this stage is called refined starch, is then
dewatered and dried. Refined starch is typically 99 % pure and 85 – 88 % dry solids. Native
starch is refined starch, before physico-chemical modification. The gluten and fibre are
collected separately as co-products. An example of a maize starch extraction process is shown
in Figure 2.18.
92 January 2006 RHC/EIPPCB/FDM_BREF_FINAL